Re: [PATCH 1/6] hugetlb: open-code hugetlb folio lookup index conversion

[jane . chu]

On 4/20/2026 11:27 AM, Matthew Wilcox wrote:
> On Thu, Apr 09, 2026 at 05:41:52PM -0600, Jane Chu wrote:
> > This patch removes `filemap_lock_hugetlb_folio()` and open-codes
> > the index conversion at each call site, making it explicit when
> > hugetlb code is translating a hugepage index into the base-page index
> > expected by `filemap_lock_folio()`
>
> I think this is too large a piece to break off in a single patch.
> The first thing I did was look at hugetlbfs_read_iter() and wonder
> why we're not able to use generic_file_read_iter() here?  It used
> to be necessary because we used to index the page cache in units
> of hsize, but now we don't, it seems to me that we could use
> generic_file_read_iter() instead.
>
> Now, what hugetlbfs_read_iter() does have is support for hwpoison
> handling.  I suspect this is something we want in
> generic_file_read_iter(), it's just nobody's done it yet.
>
> So perhaps that's patch 1 -- add hwpoison support to
> generic_file_read_iter().  Then patch 2 removes hugetlbfs_read_iter() in
> favour of using generic_file_read_iter().
>
> Patch 3 is purely this:
> (and you can put my Reviewed-by on it).
>
> > @@ -652,10 +652,10 @@ static void hugetlbfs_zero_partial_page(struct hstate *h,
> >   					loff_t start,
> >   					loff_t end)
> >   {
> > -	pgoff_t idx = start >> huge_page_shift(h);
> > +	pgoff_t index = start >> PAGE_SHIFT;
> >   	struct folio *folio;
> >   
> > -	folio = filemap_lock_hugetlb_folio(h, mapping, idx);
> > +	folio = filemap_lock_folio(mapping, index);
> >   	if (IS_ERR(folio))
> >   		return;
> >   
>
> Now for patch 4 ...
>
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index a786034ac95c..38b39eaf46cc 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -5724,7 +5724,7 @@ static vm_fault_t hugetlb_no_page(struct address_space *mapping,
> >   	 * before we get page_table_lock.
> >   	 */
> >   	new_folio = false;
> > -	folio = filemap_lock_hugetlb_folio(h, mapping, vmf->pgoff);
> > +	folio = filemap_lock_folio(mapping, vmf->pgoff << huge_page_order(h));
> >   	if (IS_ERR(folio)) {
> >   		size = i_size_read(mapping->host) >> huge_page_shift(h);
> >   		if (vmf->pgoff >= size)
>
> This points to a horrible problem.  Everywhere else in the VM has
> vmf->pgoff in PAGE_SIZE units, and of course hugetlb works in units of
> hpagesize.  So this is an entirely different piece of work where we
> convert vmf->pgoff to be in units of PAGE_SIZE.  That'll be fun!
>
> > @@ -6208,7 +6208,7 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
> >   
> >   	if (is_continue) {
> >   		ret = -EFAULT;
> > -		folio = filemap_lock_hugetlb_folio(h, mapping, idx);
> > +		folio = filemap_lock_folio(mapping, idx << huge_page_order(h));
> >   		if (IS_ERR(folio))
> >   			goto out;
> >   		folio_in_pagecache = true;
>
> This is a much smaller (more contained) problem.  At least idx is local
> to this function, so you can calculate it using linear_page_index()
> and modify the whole function.
>
> Finally, you can delete filemap_lock_hugetlb_folio():

Thanks Matthew, these are great suggestions and I am looking into them.
Main concern is potential performance impact, will find out.

Thanks a lot!
-jane

> > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > index 9c098a02a09e..c64c6e5e50f5 100644
> > --- a/include/linux/hugetlb.h
> > +++ b/include/linux/hugetlb.h
> > @@ -829,12 +829,6 @@ static inline unsigned int blocks_per_huge_page(struct hstate *h)
> >   	return huge_page_size(h) / 512;
> >   }
> >   
> > -static inline struct folio *filemap_lock_hugetlb_folio(struct hstate *h,
> > -				struct address_space *mapping, pgoff_t idx)
> > -{
> > -	return filemap_lock_folio(mapping, idx << huge_page_order(h));
> > -}
> > -
> >   #include <asm/hugetlb.h>
> >   
> >   #ifndef is_hugepage_only_range
> > @@ -1106,12 +1100,6 @@ static inline struct hugepage_subpool *hugetlb_folio_subpool(struct folio *folio
> >   	return NULL;
> >   }
> >   
> > -static inline struct folio *filemap_lock_hugetlb_folio(struct hstate *h,
> > -				struct address_space *mapping, pgoff_t idx)
> > -{
> > -	return NULL;
> > -}
> > -
> >   static inline int isolate_or_dissolve_huge_folio(struct folio *folio,
> >   						struct list_head *list)
> >   {